NGC 3115

Lore & Background

NGC 3115 is a lenticular galaxy, containing a disk and a central bulge of stars but lacking a detectable spiral pattern. It has consumed most of the gas from its youthful accretion disk, leaving very little gas and dust to trigger new star formation; the vast majority of its stars are very old. There is speculation that in its youth, NGC 3115 may have been a quasar.

In 1992, John Kormendy and Douglas Richstone announced the detection of a supermassive black hole at the galaxy's center, based on orbital velocities of stars in its core. The black hole's mass was measured at approximately one billion solar masses. The galaxy shows little or no activity, and the growth of its black hole has stopped.

In 2011, NASA's Chandra X-ray Observatory imaged a flow of hot gas toward the supermassive black hole, the first clear evidence of such a flow observed in any black hole. The gas temperature begins to rise at about 700 light-years from the black hole, marking the Bondi radius. This observation suggests a black hole mass of about two billion solar masses, supporting earlier optical results and making NGC 3115 the nearest billion-solar-mass black hole to Earth.

Reader's Guide

NGC 3115 holds significance as a nearby laboratory for studying supermassive black holes and galaxy evolution. Its central black hole, with a mass estimated at roughly two billion solar masses from X-ray observations, is the nearest such object to Earth, allowing detailed study of accretion processes. The 2011 Chandra detection of hot gas flowing toward the black hole provided the first clear observational evidence of such a flow, offering insight into how black holes grow and interact with their surroundings. The galaxy's lenticular morphology and lack of star formation illustrate a system that has exhausted its gas supply, with its black hole growth also halted. The historical misclassification as an elliptical galaxy and speculation about a quasar past add to its interest, while the single observed supernova, SN 1935B, remains poorly documented. NGC 3115 is often compared to NGC 5866, another lenticular galaxy sometimes called the Spindle Galaxy.

Did You Know?

• NGC 3115 is also known as the Spindle Galaxy and Caldwell 53.
• It was discovered by William Herschel on February 22, 1787.
• The galaxy's central black hole has a mass estimated at about two billion solar masses, making it the nearest billion-solar-mass black hole to Earth.
• In 2011, Chandra X-ray Observatory captured the first clear evidence of hot gas flowing toward a black hole in NGC 3115.